Radio frequency power amplifiers (power amplifiers for short) are widely applied to various wireless communication transmitting apparatuses. The ratio of the cost of a linear power amplifier to the cost of a base station is about 1/3, and how to effectively solve the problem of linearization of the power amplifiers with low cost will be more important. The research on a Doherty power amplifier with high efficiency and high linearity is a hot subject.
The current design of combining digital pre-distortion with Doherty power amplification has been widely applied to the power amplifiers, which greatly improves the efficiencies of the power amplifiers. The power amplifier's efficiency can reach 50%.
With the gradual maturity of a Doherty technology, design solutions for Doherty change quickly, including multi-path Doherty, asymmetric Doherty, Doherty-to-Doherty and the like. However, these technologies are updated only based on the collocation of power amplification tubes, and a traditional structural layout is still adopted. As shown in FIG. 1 and FIG. 2, according to the traditional layout of the power amplification tubes, the power amplification tubes in a Carrier path and a Peaking path are located next to each other in the same plane. Specifically, a traditional Doherty power amplifier includes a Printed Circuit Board (PCB) 1 with the length L and the width W. The input signal enters the Doherty power amplifier from a power amplifier input port 5, passes through a power divider 6, enters a Carrier power amplification tube and a Peaking power amplification tube, enters a combiner 8 for power combination, and finally reaches a power amplifier output port 7. The PCB1 can be tightly attached to a cooled metal substrate via screws or a full-page welding process, and thus the PCB1 and the metal substrate can be generally called a PCB. The height from a bottom surface of the PCB to a bottom surface of a cover plate is H. The traditional Doherty power amplifier includes 3 layers. FIG. 2 shows a side of the traditional Doherty power amplifier, including the PCB, a cavity 11 for containing a power amplification tube circuit, and the cover plate of the Doherty power amplifier.
By means of the traditional layout, the area of the plane of the PCB used by a Doherty circuit is larger, and the heat of the power amplification tubes in the Carrier path may influence the performance of the power amplification tubes in the Peaking path. The hotter the power amplification tubes are, the lower the efficiency of the power amplifier is.